Measuring Carbon Sequestration in Real-Time Under African Conditions.

Two of the biggest problems facing humankind are feeding an exponentially growing human population and preventing the negative effects of climate change and the accumulation of atmospheric greenhouse gases (GHGs).  Agriculture could address both of these problems.  For example, avoiding tillage and using cover crops increase yields by improving soil fertility and sequestering carbon (C). If one considers agriculture to be one of the biggest drivers of deforestation and land degradation, then it contributes to as much as one third of global GHG emissions.  Research can demonstrate which agricultural practices sequester C in concert with other co-benefits of increased soil fertility and crop yields, i.e., sustainability.  This is especially important where there is a lack of detailed information on farming conditions (e.g., climates and soil types) and on small farmholder practices such as in developing countries.  The study presented here was conducted in Zimbabwe, with the intent to (a) demonstrate the utility of micrometeorological methods for measuring CO₂ exchange rates between the surface and the atmosphere, and (b) to quantify differences in such exchange rates for a variety of agricultural surfaces.  Four Bowen ratio energy balance (BREB) systems were established in June 2013 on 0.64 ha sites at the International Maize and Wheat Improvement Center (CIMMYT) in Harare, Zimbabwe. The four practices were: no-till followed by planting of winter wheat (Triticum aestivum), minimum till followed by planting of blue lupin (Lupinus angustifolios L.), residue left on the surface, and residue incorporated with tillage.  Continuous micrometeorological and other environmental data were collected through October for the estimation of CO₂ flux density of the contrasting tillage and cover crop practices.  Calculations showed that the winter wheat cover crop produced a net sequestration of 257 g CO₂-C m^-2, while a tilled plot with no cover emitted 197 g CO₂-C m^-2 and an untilled plot with no cover emitted 235 g CO₂-C m^-2.  The blue lupin cover crop emitted less than both fallow plots at 58 g CO₂-C m^-2.  Our micrometeorological methods reported here can discern significant differences between treatments to identify which agricultural management practices can contribute to mitigating climate change.